This invention relates generally to clothes washing machines and more particularly, to control of the temperature of water supplied to the washing machine tub.
In at least some known washing machines, water is supplied to the machine from sources of hot and cold water such as household faucets. The washing machine includes conduits which extend from the faucets to a mixing valve, and solenoids control the mixing of water. For example, when the solenoid associated with the hot water conduit is energized, hot water flows to the mixing valve. When the solenoid associated with the cold water conduit is energized, cold water flows to the mixing valve. By selective alternate or concurrent energization of the solenoids, the passage of hot, cold, and warm water from the mixing valve to the tub is controlled.
The known mixing control described above provides acceptable water temperature if the incoming water temperature is within an acceptable range. The range for cold water typically is from 50 to 80xc2x0 F., and the range for hot water typically is from 120 to 140xc2x0 F. However, and due to temperature variations and seasonal changes depending upon geographic location, the temperature of the cold water input can drop to near freezing. In this extremely cold temperature, the detergent will not dissolve in the wash water, which can degrade performance and leave detergent residue on the clothes.
One known attempt to overcome problems associated with variations in the cold water temperature includes using an analog electronic control with a temperature sensor to control the water temperature by cycling the water valves during the fill cycle. While such cycling control provides adequate temperature control, the analog control does not limit the number of valve cycles. Unlimited cycling of the valves can cause water hammer (noise) and premature valve failure. For example, and with the known analog control, a water valve can cycle more than 40 times for a large fill with extreme water temperatures.
It would be desirable to provide a water temperature control that limits the number of valve cycles during a fill even with extreme water temperatures. Of course, even with such cycle limitation, the control should still provide the desired temperature control.
These and other objects may be attained by an automatic temperature control system which limits the total number of valve cycles for the cold and hot water valves to, for example, a total of ten cycles yet also provides the desired temperature control of water supplied to the wash tub. Particularly, and to limit the number of valve cycles, an automatic temperature control board includes a microprocessor which integrates the temperature of the water provided to the wash tub over time to predict the length of the time period required for the next water valve cycle. The integration balances the energy input on the xe2x80x9cOFFxe2x80x9d cycle with the energy input during the xe2x80x9cONxe2x80x9d cycle. Such balancing limits the number of valve cycles thereby reducing the possibility for premature valve failure and facilitating reduced noise.
In one specific embodiment, the automatic temperature control (ATC) function is operator selectable by a toggle switch mounted to the control panel. When the switch is active, the ATC system cycles either the hot and/or cold water valves to control the water temperature in the tub to within the specified range. When the ATC selector switch is deactivated, then the ATC system is disabled and the clothes washer functions in the normal mode.
The ATC control system also includes a pre-treater function. When the pre-treater function is selected, e.g., by depressing a momentary switch mounted on the control panel, and provided that the lid is open, the control system energizes the cold water valve for 7 seconds. As a result, and if COLD or WARM is selected, cold water flows into the wash tub. If HOT is selected, warm water flows into the wash tub.
In an exemplary embodiment, the automatic temperature control system includes a logic board having a microprocessor and a power supply. Generally, the board is configured to provide automatic temperature control (ATC) with the well-known electromechanical control system used in commercially available washing machines. The ATC system also includes a cold control solenoid (COLD) and a hot control solenoid (HOT). These solenoids are coupled to the valves which control the flow of hot and cold water into the washing machine tub. The system further includes a temperature sensor for sensing the temperature of water in the mixer nozzle.
Other inputs to the board include an ATC signal, a PRE-TREATER signal, a C-IN signal, and a H-IN signal. The ATC Signal is a 120 VAC signal that is active when the ATC control is selected on the control panel. When ATC is active, the system operates to regulate the inlet water temperature by controlling the water valves to achieve the desired water temperature in the tub. The PRE-TREATER signal is a 120 VAC signal which indicates whether the system should activate the pre-treater cycle. When the PRE-TREATER signal is active, the system is powered-up and remains active for 7 seconds from the time that the PRE-TREATER signal was received.
The H-IN signal is a 120 VAC signal which indicates that either the hot water or warm water setting has been selected by the operator. Warm water is selected when both the H-IN and C-IN signals are present. The C-IN signal is a 120 VAC signal which indicates that either the cold water or warm water setting has been selected. The H-IN and C-IN signals are supplied to the logic board from the control panel.
The temperature sensor input is supplied from the temperature control thermistor for measuring the temperature of the water in the washing machine mixing nozzle. Particularly, the microprocessor includes an analog-to-digital converter, and the processor reads a signal from the thermistor. The magnitude of the signal is representative of the temperature in the mixing nozzle.
With respect to the outputs from logic board, the HOT water output is a feed through of the H-IN signal to the hot water valve. The COLD water output controls the cold water valve. If the ATC signal is not active, then the C-IN signal feeds through the board to the cold control valve. When the ATC signal is active, then the ATC interrupts the C-IN signal.
Generally, the system controls the temperature of the water in the tub by regulating the inlet water flow between the hot and cold water valves. The ATC board is de-energized until the wash cycle is started and the machine is calling for water. Power is provided through the ATC select signal. On power-up, the system determines if the pre-treater or ATC function is selected. If the ATC function is selected, then the system checks the C-IN signal and the H-IN signal to determine the desired water temperature range. The system then controls the valves so that the desired water temperature is achieved.
The pre-treater function enables the operator to activate the cold water valve for a fixed duration of time while the lid is in the up position. The lid position is sensed by a lid switch which is in an open state with the lid is down and a closed state when the lid is open. When the pre-treater switch is pressed, a first relay is energized to latch on the power to the control for a period of 7 seconds. A second relay is then energized to power the cold water valve for 7 seconds. At the end of the 7 second period, the relays are de-energized to turn off the cold water valve.
To limit the number of valve cycles, the time period during which the ATC function is active is limited by a timer. Particularly, the microprocessor includes a timer, and regardless of the water temperature, the ATC function is not enabled for a timed period. When the timed period expires, the ATC function may be enabled and continue controlling the water temperature.
The microprocessor also includes an accumulator which determines how much heat, or energy, has been added above or below a desired a set point. The microprocessor controls the valve cycling based on the accumulator value, i.e., when the accumulator value is zero then the water temperature is equal to the set point temperature.
By limiting the number of valve cycles and controlling the valve cycling based on the accumulated value above or below the set point, the automatic temperature control system provides temperature control yet limits the number of valve cycles during a fill even with extreme water temperatures. Even with such cycle limitations, and as described below in more detail, the control provides the desired temperature control.